A packaging box of the kind described is generally assembled by disposing the opposite ends of the blank in overlapping relationship with each other in a region which defines the bottom of the box and adhesively bonding the overlapping portions together. Alternatively, for a packaging box in which two rows of aligned bottles are received, one end of the blank is folded to provide a partition interposed between the rows of bottles while the other end of the blank is disposed in overlapping relationship and adhesively bonded to the lower surface of the bottom adjacent to the fold line.
In either construction, the box configuration is defined by adhesively bonding the opposite ends of the blank which are disposed in overlapping relationship in a region corresponding to the bottom thereof. Accordingly, the mechanical strength of the box depends on the bonding strength, presenting a problem that boxes cannot be obtained which have a sufficient size to receive large containers or which have a sufficient strength, because of the limited material available for the blank.
To provide a rigid bond between the overlapping portions in a bottom region, it has been proposed to provide a panel of the blank which is located outside in the overlapping region and which is formed with an insert tab, which is in turn folded into an opening formed in the inner or the other panel, thus locking the both panels together. However, because the lock condition is achieved by merely inserting the tab into the mating opening, the conventional locking mechanism suffers from disadvantages that the tab is apt to be disengaged when an external force is applied and the locking action is unreliable in operation. As an overall effect, the locking means merely serves as auxiliary means to add to the strength of the bonding means provided in the overlapping region.